There is an urgent demand for sustainable and affordable alternatives to petroleum-based fuels. Biofuels are a promising replacement for petroleum-based fuels. Biofuels can be produced from animal or plant matter, such as from corn, sugar cane, sawgrass, soybeans, or algae. As such, they are a renewable and potentially limitless source of fuel. In particular, biodiesels are useful as fuel for vehicles in replacement or as a supplement to petroleum-based diesel fuels. They can be utilized by traditional fuel-burning engines, produce fewer particulates when burnt, have a higher flash point, and are less toxic than petroleum-based fuels. In 2006, biodiesel production in the United States alone was estimated to be more than 1 billion gallons.
Chemically, biodiesels primarily comprise a mixture of monoalkyl esters of long chain fatty acids. Biodiesels are typically produced from lipid transesterification of vegetable oils, including those from soybean, jatropha, palm, rapeseed, sunflower, and others; and/or animal fats with a short-chain monohydric alcohol. The longer the carbon chain of the alcohol used, the better the cold-flow properties. For example, biodiesel comprising fatty acid ethyl esters (FAEEs), derived from ethanol, has better cold-flow properties than biodiesel comprising fatty acid methyl esters (FAMEs), derived from methanol.
However, transesterification produces various unwanted side products, including saturated monoacyl glycerols (SMGs) and steryl glycosides such as steryl glucosides. Acylated steryl glycosides are soluble in oil, but during esterification, they are converted to nonacylated SGs, which are relatively insoluble. If not removed from the biodiesel, steryl glycosides can clog oil filters or cause engine failures. Particles of clumped steryl glycoside molecules can also promote crystallization, aggregation, or precipitation of other compounds in the biodiesel. This further reduces biodiesel flowability and increases the likelihood of clogging. Steryl glycosides typically have a high melting point of around 240° C. and thus cannot simply be heated to allow them to pass through an oil filter. Similarly, SMGs can form crystals in the biodiesel, especially at low temperatures, which creates cold-flow problems and can cause blockages in fuel lines under cold conditions. Additionally, the formation of these precipitates may cause several problems during the biodiesel production process resulting in an increase in production costs.
Insoluble contaminants containing steryl glycosides may appear as haze, precipitates or sediments in biodiesel, which prevents the product from complying with the requirements on contamination and filterability according to biodiesel quality standards.
One method capable of completely removing steryl glycosides and SMGs from biodiesel is distillation. Distillation is energy-intensive, which reduces the cost efficiency and net energy gain of biodiesel production. Filtering, such as through diatomaceous earth, is expensive and not easily scalable to large quantities. Adding adsorbents requires an additional removal step, and is similarly expensive and time-consuming. Other methods includes the centrifugation methods disclosed in WO 2010 004423.
Steryl glycosidases can be used to digest steryl glycosides, producing a glycoside and a sterol. Similarly, lipases can be used to eliminate SMGs. However, steryl glycosidases and lipases currently used in the field are inefficient and do not effectively reduce the amount of steryl glycosides and SMGs in biodiesel.